[HIVE-15653] Some ALTER TABLE commands drop table stats

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.1.0
• Fix Version/s: 2.3.0
• Component/s: Metastore, Statistics
• Assignee: Chaoyu Tang
• Reporter: Alexander Behm
• Created: 18/Jan/17 02:18
• Updated: 20/Sep/17 05:04
• Resolved: 31/Jan/17 16:05

Description

Some ALTER TABLE commands drop the table stats. That may make sense for some ALTER TABLE operations, but certainly not for others. Personally, I I think ALTER TABLE should only change what was requested by the user without any side effects that may be unclear to users. In particular, collecting stats can be an expensive operation so it's rather inconvenient for users if they get wiped accidentally.

Repro:

create table t (i int);
insert into t values(1);
analyze table t compute statistics;
alter table t set tblproperties('test'='test');
hive> describe formatted t;
OK
# col_name            	data_type           	comment             
	 	 
i                   	int                 	                    
	 	 
# Detailed Table Information	 	 
Database:           	default             	 
Owner:              	abehm               	 
CreateTime:         	Tue Jan 17 18:13:34 PST 2017	 
LastAccessTime:     	UNKNOWN             	 
Protect Mode:       	None                	 
Retention:          	0                   	 
Location:           	hdfs://localhost:20500/test-warehouse/t	 
Table Type:         	MANAGED_TABLE       	 
Table Parameters:	 	 
	COLUMN_STATS_ACCURATE	false               
	last_modified_by    	abehm               
	last_modified_time  	1484705748          
	numFiles            	1                   
	numRows             	-1                  
	rawDataSize         	-1                  
	test                	test                
	totalSize           	2                   
	transient_lastDdlTime	1484705748          
	 	 
# Storage Information	 	 
SerDe Library:      	org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe	 
InputFormat:        	org.apache.hadoop.mapred.TextInputFormat	 
OutputFormat:       	org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat	 
Compressed:         	No                  	 
Num Buckets:        	-1                  	 
Bucket Columns:     	[]                  	 
Sort Columns:       	[]                  	 
Storage Desc Params:	 	 
	serialization.format	1                   
Time taken: 0.169 seconds, Fetched: 34 row(s)

The same behavior can be observed with several other ALTER TABLE commands.

Issue Links

• is related to: HIVE-15742 Column stats should be preserved when it is renamed
• links to: RB